A common error in landing an aircraft is that in the transition from the flare to the touch down, the aircraft is held at an excessive height over the threshold. The excessively high position of the aircraft could be the result of an unstable approach, or a stable but high approach. It may also occur during an instrument approach where the missed approach point is too close to or at the runway threshold. Regardless of the cause, excessive height over the threshold will most likely result in a touchdown beyond the normal aiming point. An extra 50 feet of height over the threshold will add approximately 1,000 feet to the landing distance.
In an optimal landing, the aircrafts arrive at the approached threshold window exactly on altitude (50 feet above the runway). For most airports, the aircraft will pass over the end of the runway with the landing gear 30-45 feet above the surface, depending on the landing flap setting and the location of the touchdown zone. It will take 5-7 seconds from the time the aircraft passes the end of the runway until touchdown. The flare is initiated by increasing the pitch attitude just enough to reduce the sink rate to 100-200 feet per minute when the landing gear is approximately 15 feet above the runway surface.
The normal speed bleed off during the time between the passing the end of the runway and touchdown is 5 knots. Most of the decrease occurs during the flare when thrust is reduced. When the aircraft has excess energy (speed), the flare is extended (held off) so that any additional speed is bled off.
A proper approach positions the aircraft to touchdown in the touchdown target zone, which is usually about 1,000 feet beyond the runway threshold. Once the main wheels have contacted the runway, the pilot must maintain directional control and initiate the stopping process. The stop must be made on the runway that remains in front of the aircraft. The runway distance available to stop is longest if the touchdown was on target. The energy to be dissipated is least if there is no excess speed.
At the point of touchdown, the aircraft represents a very large mass that is moving at a relatively high speed. The large total energy must be dissipated by the three forces available for stopping the aircraft: wheel braking, reverse thrust, and aerodynamic braking. Of the three, the brakes are the most effective, and therefore the most important stopping force for most landings. It is advantageous for a pilot to make a touchdown “on the numbers” as to do so will leave the optimum length of runway for stopping the aircraft. Where the pilot has failed to make the touchdown “on the numbers,” the pilot must evaluate whether there remains a sufficient length of runway to stop the aircraft. Failure to judge correctly the remaining length of runway may result in runway excursion. There is an unmet need in the art for a means and a device to enhance the situational awareness of a pilot landing an aircraft particularly as to the length of runway remaining.